Thermostat with an improved heat anticipation means



April 25, 1967 c. L. NELSON 3,316,374

THERMOSTAT WITH AN IMPROVED HEAT ANTICIPATION MEANS Filed March 1, 1965 1 N VEN TOR. C1. l/ poza NELSON y y /agwmw United States Patent 3,316,374 THERMOSTAT WITH AN IMPROVED HEAT ANTICIPATION MEANS Clifford L'. Nelson, Minneapolis, Minn., assignor to Honeywell Inc., a corporation of Delaware Filed Mar. 1, 1965, Ser. No. 435,902 2 Claims. (Cl. 200-122) The present application is a continuation-in-part application of the application by Clifford L. Nelson, Serial No. 144,656, filed Oct. 12, 1961, now abandoned entitled, A Thermostat With Improved Anticipation.

The present invention is concerned with an improved heater which is used on a thermostat for heat anticipation purposes; in particular, the heater has a high heat dissipation in the low resistance range and a support member with a high thermal conductivity for a high heat dissipation to protect the heater from an excessive temperature rise when a high current flows through the heater.

FIGURE 1 is a front view of the improved thermostat showing the temperature responsive bimetal for operating the switch and the closely, thermally coupled heat anticipation heater;

FIGURE 2 is a side view of the thermostat shown in FIGURE 1 looking to the left of FIGURE 1;

FIGURE 3 is another embodiment of the heat anticipation resistance heater of the thermostat shown in FIG- URE 1;

FIGURE 4 is a sectional view of a portion of the heat anticipation resistor to show the mounting method;

FIGURE 5 is a sectional view of the resistor at 90 from the view of FIGURE 4;

FIGURE 6 is a schematic representation of the circuit used in the thermostat as shown in FIGURES 1 and 2; and,

FIGURE 7 is another embodiment of the present invention wherein the support member is a metal disc which supports a resistance windnig which is electrically insulated from the member.

Referring to FIGURE 1, the thermostat 10 has a base member 11 and a cover 12, which is partially cut away, mounted on the base in a conventional manner using a pair of clips 13 and 14 attached to the base. Pivotally attached to the base and extending perpendicularly thereto is a support post or shaft 15 which can be rotated by a lever attached to the shaft. A temperature responsive means or circular, coiled bimetal element 21 is solidly attached to shaft 15 at one extremity of the bimetal and connected to a switch supporting member 22 at another extremity 23 of the bimetal. Upon a change in temperature of the bimetal, extremity 23 moves to position a switch 24 supported on member 22. Switch 24 is a conventional mercury switch having a pair of electrodes 25 and sealed in a glass enclosure so that a circuit is closed when a small amount of mercury moves to one end of the enclosure to bridge the electrodes.

Mounted on shaft 15 at its outer extremity is a circular card support member or card-like sheet of electrical insulating material 31. Material 31 is selected to have an adequate electrical resistance characteristic and yet, material 31 should have a fairly good heat conducting characteristic. One typical material is glass melamine laminate. Support 31 is attached to shaft 15 to be supported in a plane parallel to base 11 and parallel to the plane of movement of switch 24. Mounted on support 31 is a resistance wire heater winding or heat anticipation resistance 32 which extends along the periphery of sheet 31 to surround the end of shaft 15. Wire 32 is attached to sheet 31 at one extremity by terminal 34. Along the length of wire 32 at selected points, the wire is attached to sheet 31 by looping a portionof the wire through a triangular shaped hole at points 33, 36 and 37 in a manner as shown in FIGURES 4 and 5. Referring to FIGURE 4, wire 32 is looped and the loop 38 is passed across one side and into hole 37. The lower end of loop 38 is bent fiat against the under side of sheet 31. The adjacent portions of the wire in loop 38 do not touch so the complete length of the wire in loop 38 is a part of the electrical resistance circuit of the used portion of wire 32. FIGURE 5 shows the lower portion of loop 38 as bent against the under side of sheet 31 so the wire 32 is held in place on the upper side of sheet 31 when a similar method of attachment is used at all the holes 33, 36 and 37. A wiper 40 is pivotally attached to shaft 15 by staking or rolling the end of post 15. The wiper engages wire 32 in a position selectively made by the manual movement of the wiper along the length of wire 32 in an arc-like movement. An indentation 42 on wiper 40 provides for a better electrical contact between the wiper and the wire. The position of the wiper can be set at the desired current level by a scale near the periphery of member 31.

Mounted on base 11 is. a pair of terminals 50 and 51 which provide suitable connections for an external circuit, as shown in FIGURE 6, for the thermostat which could include a load device or relay 46 having an energization winding 49 and a source of power or transformer 47 having a secondary 48. A series circuit is connected between terminals 50 and 51 which can be traced in FIG- URE 1; or in the schematic circuit of FIGURE 6 as follows: from terminal 50, wire 52, shaft 15, wiper 40, wire 32, terminal 34, wire 53, electrode 30 and electrode 25 of switch 24, wire 54, and back to the other terminal 51. The circuit in FIGURE 6 shows a load device or relay and -a source of power as a transformer secondary.

Also mounted on the thermostat base is a conventional bimetal temperature indicating device comprising a bimetal 60 which is attached to the base and to a pointer 61 cooperating with an index on a panel 62 attached to the base. Connected to the lower end of member 20 is a pointer 63 which cooperates with the index on panel 62; so that, when the extreme end 64 of member 20 is manually moved, the temperature to be controlled can be selected by positioning shaft 15 and one end of the bimetal.

Referring to FIGURE 3, another embodiment of the anticipation heater shown in FIGURE 1 has a support member 131 which is connected to shaft 115. A printed circuit heater winding 132 is connected between terminals 133 and 134 in a circular manner. A movable wiper attached to a shaft.115 is manually positioned; so that, an indented portion 142 on member 140 engages the printed circuit winding. By the selection of the position of memher 140, the amount of resistance winding 132between the member 140 and terminal 134 in the circuit shown in FIGURE 6 is selected for heat anticipation purposes. When Wiper 140 is moved along resistance 132, the wiper engages the resistance along the outer ends of each loop to provide for a larger resistance length by extending each loop inward.

Referring to FIGURE 7, another embodiment of the present invention comprises a support member which may be supported on the shaft 15 of the thermostat as shown in FIGURE 1. Member or card 150 has a good thermal heat conductivity characteristic and might be made out of sheets of metal such as aluminum. The surface 151 of the member is anodized or coated to provide an electrical resistance coating; so that, a printed circuit wiring network or heater 152 can be placed on the member 150 to be electrically insulated from the member. The circuit 152 has a terminal connection 153 so that a circuit is provided from end 153 to a wiper which moves along the outer periphery of the electrical circuit. Varying amounts of electrical resistance between the end 3 153 and the wiper is used in the same manner as the heater as shown and described in FIGURES 1 and 3.

With the support of heater 152 on aluminum, the heat is conducted rapidly to the temperature responsive means. The rate of heat transfer establishes a time constant which is indicative of the thermostat offset. With the support being thermally connected to the support shaft, the heat transfer to the bimetal has a relatively constant time constant at different settings of the wiper. For this reason the system offset or droop is unaffected by different current settings of the wiper.

The printed circuit 152 comprises a first portion 154 which is quite wide to have a low resistance and as the circuit moves along from the end 153 to the other extreme end 155, the cross-section width of the circuit becomes narrower and the resistance per unit length becomes greater until at other end 155 the circuit is quite small. By means of the wide portion 154, the heater is capable of dissipating a considerable amount of heat to member 150 to provide for a high current capacity should an abnormal condition exist.

During the installation of such a thermostat in a circuit as shown in FIGURE 6, the installer can modify the circuit in various ways to test the operation during which time an excessive current would be caused to pass through the heater winding 32. For example, if the relay winding 49 is shunted by a screwdriver or some other means to cause the relay to drop out for test purposes, the impedance of the circuit is changed and the cunrent through heater winding 32 may be quite large. If when such a test operation is done and the position of the wiper on the impedance winding is close to the connected end; that is, the wiper would be closed to the end 153 of the element in FIGURE 7, a large current would pass through the resistance winding. With a low amount of resistance in the heater winding, the current would be quite high and if the resistance winding is not capable of dissipating the heat which then exists, the winding will burn out. By making the resistance winding so that conductor is quite wide to provide for the dissipation of the heat, such a resistance winding is capable of withstanding such short circuits as might be imposed on the heater.

Printed circuit 152 has a second portion 160 made up of a plurality of loops. Second portion 160 has a slightly higher resistance per unit length than first portion 154. By the difference in resistance per unit length, a scale similar to FIGURE 1 associated with portion 154 of FIG- URE 7 can be expanded at the high current or first portion and to allow for easier adjustment and a readable scale.

Operation When a relay or some control device and a source of power are connected in series between terminal 51 and 50 of thermostat 10, as shown in FIGURE 6, a current circulates through the active portion of the heater between terminal 34 and wiper 40 when switch 24 is closed as shown in FIGURE 1. When bimetal 21 calls for heat and the extremity 23 moves to the left to tip switch 24 so that electrodes 25 and 30 are shorted, a current passes through the active portion of resistor 32. The active portion with the wiper as shown in FIGURE 1 includes the looped portion of wire 32 which extends into hole 36 to hold the wire on card 31. The heat developed by the resistor is transmitted to the bimetal to artificially heat the bimetal. As the bimetal increases in temperature due to-the artificial heat, switch 24 is moved to the right to open the circuit to anticipate the increase in temperature in the space in which thermostat is mounted. The

use of the heat from a heater mounted close to the temperature responsive element 21 is quite commonly known as heat anticipation.

In the thermostat shown in FIGURE 1, the heat from the active portion of winding 32 is transmitted to bimetal element 21. The thermal path for this heat can be through the member 31 by conduction to shaft 15 and then to bimetal 21 and by radiation from member 31 to bimetal 21. The thermal path through member 40 and shaft 15 into the bimetal is also used to conduct the heat from heater 32 to the bimetal 21. With the heater 32 closely associated with the bimetal 21, an even distribution of heat for heat anticipation purposes is provided. When the material for member 31 is selected, the electrical resistance between heater 32 and the support must be high enough; however, the member 31 is selected to have a heat conducting characteristic sufficient to provide proper operation. With a high heat transfer characteristic heat from any part of wire 32 can be conducted directly to shaft 15 to provide a low time constant which decreases the droop of the thermostat.

Referring to the heater embodiment shown in FIGURE 3, the active portion of heater 132 between member and terminal 134 is used in the same manner to provide heat to the bimetal. The bimetal is mounted adjacent member 131 as shown in FIGURE 1 with the first embodiment of the invention.

While the thermostat heater of FIGURE 1 and FIG- URE 3 is mounted on a card of material which has a thermal heat conducting path through the card and through the wiper to the shaft and thus to the bimetal as well as providing a radiation surface so that heat can be radiated to the bimetal. The heater of FIGURE 7 has a member which has an even larger thermal conductivity characteristic; so that, as the heat is produced by the current passing through the circuit mounted on the member 150, the heat is conducted into the member and through the member to the shaft to pass through the bimetal. The heat also conducts throughout the member to provide that the member has a more even temperature so that the heat can radiate to the bimetal.

In the operation of a heat anticipation heater for a thermostat, the time constant, that is the time required for the heat to pass from the heater to the bimetal must be as low as possible to provide for the minimum amount of offset or droop. With the present heater design, no matter what the position of the wiper is to select the various values of resistance in the heater winding, the heat can pass from the resistance winding into the member 150 as shown in FIGURE 7 to be readily conducted to the shaft and then to the bimetal or be conducted throughout the member 150 to provide a constant tempertaure heat radiating source to the bimetal. In other types of thermostat heaters, the time constant of the heat anticipationheater often varies with different sizes of the heater resistance; so that, for different values of the heater, the offset or droop of the thermostat is changed. The present heater not only provides for relatively constant droop characteristic at various settings of the heater, but the heater has a physical size which provides for the mounting of the heater on the free extremity of the bimetal shaft to make the heater and bimetal unit relatively compact in size which is very important when the overall size of the thermostat is to be maintained at a minimum.

While the present invention has been shown in one particular manner, the intention is to limit the invention only by the scope of the appended claims.

I claim:

1. A thermostat comprising, temperature responsive means, a base, a resistance heater, a support member mounting said heater having a relatively high thermal conductivity, common support means connected to said base for supporting said responsive means and said support member on said base so said heater is adjacent said responsive means, said support means and said support member providing a heat conduction path between said heater and said responsive means, switch means operably connected to said responsive means, and circuit means adapted to connect said switch means and said heater to a source of power whereby said heater applies heat to said responsive means when said switch operates for anticipation purposes, said heater comprising a first portion and a second portion connected in series, said first portion being a low range resistance portion, an adjustable connection for selecting the amount of said heater to be energized, said first portion having a large physical dimension increasing the surface area per unit length to increase the heat dissipation whereby upon a predetermined high current passing through said first portion, the temperature of said first portion will be limited to a predetermined value by the loss of heat from said support memher.

2. An improvement in a thermostat having a base, temperature responsive means, a support connected to said base, means connecting said temperature responsive means to said support, adjustable heater means, support means mounting said heater means, and circuit means adapted to connect said heater to a source of power when said responsive means calls for a change in temperature, the improvement comprising said heater means having a larger surface area for a high heat dissipating characteristic in the low resistance range and said support means having a relatively high thermal conductivity to provide for heat dissipation by radiation whereby at low resistance settings of said heater means excessive current cannot develop suflicient heat to overheat said heater means.

References Cited by the Examiner UNITED STATES PATENTS 853,784 5/1907 Heath 338-310 1,881,445 10/ 1932 Flanzer et al 252-506 2,486,148 10/1949 Glynn et a1. 338-308 X 2,679,569 5/1954 Hall 117-226 2,705,749 4/1955 Daily et a1. 338-174 2,744,986 5/ 1956 Caldwell 338-142 X 2,798,140 7/1957 Kohring 338-142 X 2,847,536 8/1958 Bishop 200-122 3,051,001 8/1962 Laviana et al. 200-122 X 3,087,032 3/1963 Fleury 2 00-122 3,154,654 10/1964 Woods et al. 200-122 FOREIGN PATENTS 584,477 1 0/1959 Canada.

BERNARD A. GILHEANY, Primary Examiner. T. MACBLAIN, H. A. LEWITTER, Assistant Examiners. 

1. A THERMOSTAT COMPRISING, TEMPERATURE RESPONSIVE MEANS, A BASE, A RESISTANCE HEATER, A SUPPORT MEMBER MOUNTING SAID HEATER HAVING A RELATIVELY HIGH THERMAL CONDUCTIVITY, COMMON SUPPORT MEANS CONNECTED TO SAID BASE FOR SUPPORTING SAID RESPONSIVE MEANS AND SAID SUPPORT MEMBER ON SAID BASE SO SAID HEATER IS ADJACENT SAID RESPONSIVE MEANS, SAID SUPPORT MEANS AND SAID SUPPORT MEMBER PROVIDING A HEAT CONDUCTION PATH BETWEEN SAID HEATER AND SAID RESPONSIVE MEANS, SWITCH MEANS OPERABLY CONNECTED TO SAID RESPONSIVE MEANS, AND CIRCUIT MEANS ADAPTED TO CONNECT SAID SWITCH MEANS AND SAID HEATER TO A SOURCE OF POWER WHEREBY SAID HEATER APPLIES HEAT TO SAID RESPONSIVE MEANS WHEN SAID SWITCH OPERATES FOR ANTICIPATION PURPOSES, SAID HEATER COMPRISING A FIRST PORTION AND A SECOND PORTION CONNECTED IN SERIES, SAID FIRST PORTION BEING A LOW RANGE RESISTANCE PORTION, AN ADJUSTABLE CONNECTION FOR SELECTING THE AMOUNT OF SAID HEATER TO BE ENERGIZED, SAID FIRST PORTION HAVING A LARGE PHYSICAL DIMENSION INCREASING THE SURFACE AREA PER UNIT LENGTH TO INCREASE THE HEAT DISSIPATION WHEREBY UPON A PREDETERMINED HIGH CURRENT PASSING THROUGH SAID FIRST PORTION, THE TEMPERATURE OF SAID FIRST PORTION WILL BE LIMITED TO A PREDETERMINED VALUE BY THE LOSS OF HEAT FROM SAID SUPPORT MEMBER. 